Without prejudice to the matter of whether it is appropriate for blessings to be offered in lieu of communion, it is worth stating that the document you quote has no proper standing, having been propagated largely via the internet and via photocopies passed from one person to another.
As I’m sure someone with as extensive a knowledge of liturgical matters as yourself must know, changes to liturgical norms or practice, whether they emerge from the Holy See or within a Particular Church, must be communicated through proper means, without which they have no legal force. This letter does not meet the required standard.
Since you would be wise not to take my word for it

and indeed since all of us would be wise not to simply take the word of a poster on CAF with regard to any matter (!) you might wish to read the EWTN item on this subject which emphasises that the letter has no legal force. See:
ewtn.com/Library/Liturgy/zlitur263.htm
Canon law is explicit on this issue (see canons 26-75 at
vatican.va/archive/ENG1104/__P5.HTM for the laws on process in all their glory.
The intent is precisely to avoid the confusion that will emerge if legal changes are made in an extra-legal way. A proper process for instructing the People of God is not useless red tape, but a safeguard against misunderstanding and the risk of change being introduced via assumption or inference rather than in the prescribed manner. If the dicastery chooses to mandate such a change, they will be obliged to do so in the manner that canon law requires. A response to a private query, which is what the letter you quote was, does not meet those requirements.
I repeat that this is without prejudice to whether the practice of giving blessings is advisable or not. However, it is not helpful to express the thoughts or even the clear preferences of the Congregation for Divine Worship as legally binding until a legal instruction has been issued by them. They may do this tomorrow, in which case this discussion is moot. Or they may never do so.
As you state yourself, the letter contains observations, not instructions. And I realise that some people would prefer to embrace such observations irrespective of whether or not they become legally binding. That would be their right, but there is no concurrent right to say that - as you put it - ‘Rome has stated’ that blessings should not be happening and that ignoring same is tantamount to disobedience or ignorance of liturgical norms. Although you didn’t use those terms, and may not have intended such a reading, they are perhaps implied in the choice of words you did use, in my humble opinion. I think it would be a mistake to make clergy or EMHCs think that they were enacting a practice proscribed by the Holy See when this is not in fact the case